Cathode-ray storage tube



Patented Nov. 23, 1948 Our invention relates cameos-nay sronAGE TUBE particularly to tubes of the type having a signal storage screen which is scanned by a cathode ray beam. More specifically, the invention relates to signal storage tubes in which a signal is put on the storage screen by one electron beam and taken off the screen by a second electron beam;

An object of the invention is to provide an improved tube of the above-described type.

Another object of the invention is to provide a tube of the above-described type wherein the storage elements of the storage screen each have comparatively large capacity so that they can store a substantial amount of energy when raised to a potential of only a few volts.

Still another object of the invention is to provide a tube of the above-described type which is of simple mechanical construction and which also has the desired electrical characteristics.

In one preferred embodiment of the invention the storage screen comprises capacity or storage elements formed by a large number of horizontal strips of platinum or other metal on the scanned side of the screen. Two electron guns are positioned opposite the screen and separate deflecting means are provided for deflecting each electron beam vertically across the metal strips. Thus, one beam may be utilized to put a signal on the screen and the other beam may be utilized to take the signal oif the screen. By deflecting the two electron beams at different rates, the frequency of the signal may be increased or decreased as desired. By deflecting the beams in different time 2 cri a nd take-off beams are high and low velocity beams, respectively.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Figure 1 is a plan view, partly in section, of one tube embodying the invention.

Figure2 is a view taken on the line II-II in Fig. 1, and

Figures 3 and 4 are fragmentary views, in plan and section, respectively, of the storage screen or target in the tube of Figs. 1 and 2.

Referring highly evacuated envelope having a bulb portion III, in which a storage screen II is mounted, and having two neck portions l2 and I3 in which are mounted a high velocity beam put-on gun and a low velocity take-off gun, respectively.

The high velocity and low velocity electron guns may be of well known types such as those to the drawing, the tube comprises a to athode ray and m y Iams,-Albert Gardner L. Kricger, Princeton; N. 1., assignors to Radio 001'- poration of Americana corporation of Delaware Application June 26, 1943, Serial No. 49255:: "9 (orator-o) t r. 2 employed in the high velocity beam and low velocity beam television pick-up tubes known as the iconoscope and the orthicon; respectively. In

the example illustrated, the high velocity gun comprises a cathode l6, a control grid II, a first anode l9 and a second anode 20. A collector electrode 2| is provided to collect secondary electrons from the storage screen ll. Vertical deflection of the "put-on beam may be produced by means of a pair of deflecting plates 22. Horizontal deflec ing plates 25 maybe provided for a preliminary beam focusing adjustment as described hereinafter. Operating voltages that may be apbe formed, for example, by sputtering a conducting coating of platinum upon each side of the mca sheet and then scratching about lines to the inch on the front or scanned side with a ruling machine to separate the metal into conducting lines. The metal coating 25 on the back side of the m ca sheet may be used as the signal plate for taking off the signal, if desired. A strip of fluorescent material 21 may be put on an edge of the target to aid in focusing the electron beam.

A silver evaporator 28 isprovided to coat the screen during the processing of the tube to make the secondary emission uniform over the whole line surface. The amount of silver introduced is too small to make the space between the lines 24 conducting. A small amount of caesium may also be supplied through a tube 29 to make sure that the ratio of secondary electrons to primary electrons is greater than unity. Since it is preferred that the screen ll shall not be photoelectric, no oxidizing step preceding the introduction of caesium is required, as would be the case in processing a mosaic screen for an iconoscope.

The screen II when mounted in the tube preferably is curved to conform to the surface of a cylinder having an axis that passes through or near the centers of deflection of the two electron beams whereby the point of smallest beam diameter is always at the screen surface as the beam is deflected and whereby the beams during deflection are substantially at right angles to the screen surface where the beam strikes. The latter feature is important in the operation with a low velocity beam.

In operation, the incoming signal is applied to the control electrode I! to modulate the intensity of the high velocity beam as it is deflected vertically across the conducting strips. The number of secondary electrons liberated from the strips exceeds the number of beam electrons and, since substantially all of the secondary electrons are drawn over to the collector electrode 2 I, they are not redistributed over the target. Hence, the bombarded strips 24 are given a more positive potential.

At the other end of the screen I I the conducting strips are scanned by deflecting the low velocity beam vertically by means of a deflecting coil 30, for example. The electrons of this beam strike the conducting strips 24 with a velocity so low that the ratio of secondary electrons to primary or beam electrons is less than unity. According to onepreierred method of operation, sufllcient beam current is provided to return the conducting lines to the potential of the cathode supplying the low velocity beam. Thus the signal put on by the first beam is substantially completely wiped ofi" by a single scanning of the second beam. Under certain conditions it may be desired to operate the tube with a low velocity beam of less current density so that the beam removes only a small percentage of the stored signal as it scans once across the screen. The beam current may be reduced by applying a more negative bias to the control electrode 31 referred to below. At the same time it may be desirable to reduce the amplitude of the signal that is modulating the high velocity beam.

The output signal produced by this wip n off may be derived from an electrode or from an electron multiplier receiving the unused electrons of the take-off beam as they return from the screen II. These methods of taking off a signal from a storage screen are Well known in connection with iconoscopes and orthicons. If the second method of taking oi the signal is employed, the tube is provided with a mica partition 3I to prevent secondary electrons produced by the put-on beam from reaching the electron multiplier or collector electrode at the other side of the tube. Also, a ring electrode 32 near the partition may be provided and held at a negative potential to repel any secondary electrons that might otherwise get past the partition.

In the example illustrated, the low velocity beam electron gun comprises a cathode 36, a control electrode 31, a screen grid 38, a first anode 39 and a second anode 4|. Two frame-like electrodes 42 and 43 are positioned between the second anode II and the screen I I for slowing down the electrons after they leave the region of the second anode.

If thesignal is to be taken ofi by an electron multiplier a secondary electron emissive plate 46 is provided, the plate having a slit through which the electron beam passes. A wire screen 41, also having a slit through which the beam passes, collects the electrons released from the secondary emissive plate. It will be understood that the screen 41 may 'be omitted and the signal taken off by the plate 46 without electron multiplication, if desired. In either case, electrons in the lowvelocity beam which are not used in dischargingthe screen elements 24 are reflected, and may be made to strike the multiplier plate either by use of a magnetic field (not shown) at right angles to'the magnetic deflection field provided by the coil 30 or by positioning the axis of the electron 4 gun at a slight angle with respect to the perpendicular to the screen I I.

Proper focusing of the high velocity electron beam is greatly facilitated by applying a steady deflecting voltage to the deflecting plates 25 to make the beam strike the strip of fluorescent material 21. The size of the beam spot can then be observed so that the electrode voltages can readily be adjusted to obtain a spot of minimum diameter.

Proper adjustment of the vertical deflecting coils at the low velocity beam side of the tube is facilitated by applying a coating 48 of fluorescent material to the side of the plate 46 facing the electron gun. The fluorescent coating 48 makes it possible to observe whether the vertical .trace of the beam is exactly vertical and whether it is centered to deflect along the slit in the plate 48 so that all of the beam will pass through the slit.

We claim as our invention:

1. A signal storage tube that comprises a storage screen comprising a multiplicity of discrete parallel conducting strips which have a secondary emissive ratio greater than unity when scanned by a high velocity beam, means for scanning transversely across said strips by a high velocity electron beam, means for collecting secondary electrons released by said beam, means for scanning transversely across said strips by a low velocity beam with the electrons striking said strips with a velocity so low that the ratio of secondary electrons to beam electrons is less than unity, means for modulating one of said beams by an input signal whereby it is stored on said screen, and means for collecting the signal removed from the screen by the other beam.

2. A signal storage tube that comprises a storage screen comprising a multiplicity of discrete parallel conducting strips which have a secondary emissive ratio greater than unity when scanned by a high velocity beam, means for scanning transversely across said strips by a high velocity electron beam, means for modulating said beam by a signal, means for collecting substantially all of the secondary electrons released by said beam. means for scanning transversely across said strips by a low velocity beam with the electrons striking said strips with a velocity so low that the ratio of secondary electrons to beam electrons is less than unity, and means for collecting the signal obtained by said low velocity beam scanning.

3. A signal storage tube that comprises a storage screen comprising a multiplicity of parallel conducting strips, means comprising an electron gun for scanning transversely across said strips,

means for modulating said beam by a signal,

means comprising a second electron gun for scanning transversely across a different portion of saidstrips, and means for collecting the signal obtained by said last beam scanning, said screen being curved to conform substantially to the surface of a cylinder having its axis passing through the centers of deflection of said beams, the conducting strips being substantially parallel to said axis.

4. The invention according to claim 3 wherein there is a strip of fluorescent material on said screen at right angles to said strips and at one side of the screen area scanned by a beam during operation 01 the tube, and means for deflecting the high velocity beam to make it strike said fluorescent material whereby the beam spot may be observed to facilitate beam focusing.

conducting strips, means comprising an, electron gun for deflecting a 'high' velocity electron beam transversely across-said: strips,-,-,-means or modulatingv said .bea by a signal; means jv compris- I ingan electron gun-ator"scanningtransversely across a diflferent. portion; of said strips, .rneans for collectingfthe'signal, obtained-Lb?!" said last beam scanning, said-screen being curved.- to conform substantially to-the surface of;.- ylind r having its axis-passing throughfl'the centers oi cent materialon said storage; screen transverse tofsai'dconductingy'strips'in a region that is not struck by :an.-.,electrongbeam-during.the tube opmamiendmeaa a highfveiocityie cc 6 ulating said beam-byan in ning transversely across ,lsaifdjel'ernentsby a low velocity beam havingjsufflcien current density to remove, substantially all: the; stored J signal from" obtained by said last-scanninggun for deflecting-a transversely-across aidstrip's" means for modulatingsaidbeam byarsig a jeans comprising an electron gun-,idrj deflectingialbw velocity electron beam transverselyacrossa different portiondeflection off; said beams, that-conducting; I strips being parallel-t0said-axis; a d a-stripof' fluores:

neck portions for scanning. 'transversely across said strips by a high velocity electron beam, means for collecting secondary electrons released by said beam, means in the-other of said neck portions for ,scanning transversely across said strips attheother e'nd of the'bulb portion by a low velocity beam withthejelectrons striking said strips with avelocity'so low that the ratio of secondary electrons to beam electrons is less than unity, a partition separating, the two end portions ofthe bulb portion, means for modulating one of said beams by an input signal whereby it is stored on said screen, and means for collecting the signal Y removed from the screen by the other beam.

9. ,A signal storage tube having a bulb portion and two'neck portions, a storage screen located I j insaid.bulb-portion, said screen comprising a sfor-deflectingland holding said;

id uores'cent strip";

P & aps'toraee {discrete sec-'- multiplicity of parallel conducting strips which,

at-Oneend'of the bulb portion, have a secondary emissiv'e'ratio greater thanunity when scanned said' strips by a -high velocity electron beam,

id elements by means: formed nut i n wh er h -fl signal is stored on; said screen, 1 means .1forscan-I :means'for collecting-the secondary electrons releasedfiby said beam, means in'the other of said neck portions for scanning transversely across Ksaid strips-j at the other end of the bulb portion said screen, and means .for' collectingpthe signal by a low velocity beam with the electrons striking said stripswith a velocity so;low that the ratio of secondary electrons 'to beam; electrons is less than unity, a partition separating the-two end portions of the bulb portion, means for modulating saidhigh velocity beam by an input signal whereby it is stored on said screen, and means for collecting the signal removed from the screen by. the low velocity beam, said low velocity beam having sufficient current density to remove the stored signal completely from the storage screen.

of said strips, means-for collecting the signalobtained by said last beam scannlng '-said lo'wf'veloc ity beam having. sufficient current density-to re-. move the stored signal completely 'from said screen, said'screen being curved to conform sub-- stantially to the surface of a cylinder havingits axis passing through the centers of deflection of said beams, the conducting strips being substanat one end of the bulb portion, have-,alsecondary emissive ratio greater than unity-whensjcanned I by a high velocity beam, meansin-one oi said j HARLEY IAMS. ALBERT ROSE.

. GARDNER L. KRIEGER.

REFERENCES CITED The following references are of record in the file of this patent: on

UNITED'STATES PATENTS Number Name Date 2,072,658 Von Bronk Mar. 2, 1937 2,122,095 Gabor June 28, 1938 2,147,760 Vance et al Feb. 21, 1939 2,179,205 Toulon Nov. 7, 1939 2,254,128 Bosch Aug. 26, 1941 2,301,743 Nagy et al Nov. 10, 1942 2,367,277 Henroteau Jan. 16, 1945 

